Doping ZIF-67 with transition metals results in bimetallic centers for electrochemical detection of Hg(II)

Abstract

Development of robust methods for rapid detection of heavy metal ions and associated chemical species in water is challenging. Different mercury species are ubiquitous in the environment; they bio-amplify and undergo methylation into organo-Hg species. We developed a new electrochemical method for rapid screening of free Hg2+ in water by square wave anodic stripping voltammetry (SWASV) on a metal-organic framework (MOF) platform using ZIF-67 as starting substrate. Bimetallic MOF structures were fabricated by doping iron, manganese or nickel ions into ZIF-67 using a facile NaOH treatment. The GCE was modified with Ni, Mn, or Fe doped ZIF-67 nanocomposites to enhance performance for Hg2+ detection. When compared to pure ZIF-67/GCE, the Hg2+ detection sensitivity by the metal ions-doped ZIF-67/GCE was increased by 260%. The detection limit was improved by 60%. The Fe doping on ZIF-67 (FexCoy) significantly improves electroanalytical performance due to the formation of iron oxide on ZIF-67. The GCE modified with Fe1Co1 nanocomposite showed the best performance for electrochemical detection of Hg2+. Besides, the cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) data also confirmed that Fe doping of the ZIF-67 enhanced the electron transfer rate at the solid-liquid interface. Hg2+ detection and quantification at this new chemically modified sensing electrode were not interfered by Cd2+, Pb2+, and Cu2+. The Fe1Co1 modified GCE is stable when used repeatedly for ten cycles. The spike recovery of 0.3 to 1.00 µM Hg2+ with Fe1Co1 modified GCE was always above 99.0%. The chemically modified sensor with Fe1Co1 holds a promise in monitoring Hg2+ at trace concentrations.